Rotary helical splined actuators have been employed in the past to achieve the advantage of high-torque output from a simple linear piston-and-cylinder drive arrangement. The actuator typically uses a cylindrical body with an elongated rotary shaft extending coaxially within the body, with an end portion of the shaft or the body providing the drive output. An elongated annular piston sleeve has a sleeve portion splined to cooperate with corresponding splines on the body interior and the shaft exterior. The piston sleeve is reciprocally mounted within the body and has a head for the application of fluid pressure to one or the other opposing sides thereof to produce axial movement of the piston sleeve.
As the piston sleeve linearly reciprocates in an axial direction within the body, the outer splines of the sleeve portion engage the splines of the body to cause rotation of the sleeve portion. The resulting linear and rotational movement of the sleeve portion is transmitted through the inner splines of the sleeve portion to the splines of the shaft to cause the shaft to rotate relative to the body. Bearings are typically supplied to rotatably support one or both ends of the shaft relative to the body.
While such an arrangement produces a relatively high-torque output, the capability of the actuator to support high moment loads and large axial and radial thrust loads has been limited. The actuator typically has a slender shaft with bearings between the shaft and end flanges or end caps of the body, with the bearings positioned radially inward of the body sidewall. It is desirable to use rotary actuators to rotate heavy tools, such as grapples and shears, which are subjected to large loads.
The conventional rotary actuator is not well constructed to handle the high moments often encountered when used as a tool actuator. Further, the axial thrust loads encountered due to the weight of the tool, and the load it carries, may be too great for conventional actuator bearing configurations.
Another problem involves the cost of manufacturing actuators, especially ones designed to handle high moments and large axial and radial loads. As shown in the inventor's U.S. Pat. No. 4,881,419, in the past the actuator body has been designed with a thick wall construction, and since the bearing races are formed in the body sidewall of the actuator, the body must be hardened. The result is a heavy and expensive body. Even in lighter load applications where a thin-wall body construction is used, end caps with a plurality of the rods extending therebetween are often needed.
When using a rotary actuator to carry a tool, such as a grapple or a shear which operates on pressurized hydraulic fluid, delivering the fluid to the hydraulically operated cylinders which operate the moveable arms of the grapple or the movable jaw of the shear becomes difficult. With a grapple, it is desirable to have the actuator shaft fixedly attached to an attachment head which can be carried at the end of a boom arm of a vehicle, with the arms of the grapple pivotally attached to the actuator body. The movement of each arm may be accomplished using a hydraulically operated cylinder which extends between the arms and the actuator body to cause the arms to pivot relative to the body. In such manner, the arms of the grapple can be caused to open and close. Since the actuator body is rotated on the fixed actuator shaft, and thus relative to the attachment head to which the shaft is fixedly attached, it becomes difficult to supply pressurized hydraulic fluid to the cylinders which operate the grapple arms.
Use of flexible pressure hoses to carry the hydraulic fluid from the source of pressurized hydraulic fluid, usually supplied by a pump mounted on the vehicle, requires that hoses extend along the vehicle's boom arm and then to the cylinders. While each hose can be provided with a large loop of hose to allow for the rotation of the actuator body and the grapple arms attached thereto without twisting of the hoses, such loops of hose can become entangled or snag on obstacles while the grapple is being operated. This can result in pinching or breaking of the hoses. Of course, when this occurs the operator must untangle the hoses or, if damaged, replace them, resulting in unproductive time. Further, if a hose is broken, the loss of hydraulic pressure might cause the grapple to drop the load being carried, resulting in damage.
In the inventor's earlier U.S. Pat. No. 4,342,257 showing a tool actuator, a coupling block is used to provide the fluid connection between a tool attached to the end of the actuator shaft and the coupling block. The coupling block is rigidly connected by bolts to a stationary body which is affixed to a boom attachment head. A hydraulically operated cylinder is connected between the coupling block and the boom of a vehicle carrying the actuator. While this arrangement provided an improvement over the prior art, during operation of the tool, the forces applied to the coupling block by the cylinder to move the assembly about, and forces on the shaft that produced as the tool was operated, caused undesirable movement between the coupling block and the shaft. This resulted in difficulty in achieving a good fluid seal between the coupling block and the shaft and increased seal wear.
It will therefore be appreciated that there has long been a significant need for fluid-powered rotary actuators capable of handling increased moments and axial and radial shaft loads. The actuator should have a compact and lightweight design which allows use of a thin wall body construction without requiring use of tie rods. The actuator should be economical to manufacture. Further, the actuator should provide a convenient means for transmitting fluid pressure between a vehicle-carried pressurized fluid source and a tool which is attached to a rotatable actuator body with minimum resulting seal wear and improved sealing to eliminate leakage of pressurized fluid. The present invention fulfills these needs and further provides other related advantages.